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LM317 adjustable Voltage reg. with Led voltage level indicator question

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Hi All

I'm looking for info and guidance for a voltage regulator circuit I require.Basically as you can see from the title I'm looking at using a LM317 (because I have them) but I'm wanting to add a number of LED's to indicate when an adjusted voltage level is reached.

I've looked at using zener diodes but after testing I've not yet achieved what I require.

I have 24v 800ma input on the LM317 and I'm hoping to indicate the Vout via the led's from around 3v and then in multiples of 3v using 8 LED's in total, 3v output first LED lights up, 24v all eight light up (or something along those lines)

There maybe simpler methods or IC's but I'm unsure of the best practical way to do this.I would like to use my LM317 as I have them.

Many thanks
 
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I would think about using a LM3914. That or building your own stack of window comparators using several LM339 comparators but the single LM3914 should get you where you want to go.

Ron
 
I'd put an analog meter movement on it. I know it's not what you asked but it has MUCH better resolution (as a voltameter it functions much better) and is very simple to add.
 
Hi wombweller,

I hope you are aware of the fact that an LM317 requires ~2V above the stabilized output voltage.

So at +24V input the output voltage is max 22.2V (ideally).

Also getting that span into an LM3914 for indication in steps of 3V is a bit complicated, if at all possible.

I designed a circuit using all ten LED outputs stepping from 2V to 20V with each LED (2V per step).

22V indication is omitted since there is not much to interpret if the voltage selector is at maximum.

You might use the flashing function of the LM3914 to indicate an input voltage >20V.

With the circuit dimensioning the LED current will be approximately 10mA.

Boncuk
 

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Hi wombweller,

I hope you are aware of the fact that an LM317 requires ~2V above the stabilized output voltage.

So at +24V input the output voltage is max 22.2V (ideally).

Also getting that span into an LM3914 for indication in steps of 3V is a bit complicated, if at all possible.

I designed a circuit using all ten LED outputs stepping from 2V to 20V with each LED (2V per step).

22V indication is omitted since there is not much to interpret if the voltage selector is at maximum.

You might use the flashing function of the LM3914 to indicate an input voltage >20V.

With the circuit dimensioning the LED current will be approximately 10mA.

Boncuk

Hi Boncuk!!

I did take that into account but it don't mean I don't need the heads up just in case!!

Neat little circuit I might just give that ago.

This is just a little something for my uncle who has some electric clocks that need variable output.I'm going to use my press & peel pcb. system to make a plaque to show the numeric output voltage.

Many thanks!
 
Hi Mark,

here are schematic and board design for your power supply.

Both PBCs are purely single sided.


I used a total of 9,400µF smoothing caps for low ripple voltage. You might omit one of them and still have good DC output.

Remove C2 if you want to reduce capacitance.

If you want the Eagle files please PM me your email address.

Regards

Boncuk
 

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Sir, can you please help me too. Here is my power supply design. I dont know how will i put lm3914 to my power supply. Output is from 1.25-30V. Thanky you.
 

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